Clinical evaluation of the efficacy of three nitrous oxide scavenging units during dental treatment - [N.sub.2]O

Dental Assistant, The, March-April, 2003 by Fred Certosimo, Martin Walton, David Hartzell, Jennifer Farris

There are environmental health concerns for dental health care providers chronically exposed to trace amounts of waste nitrous oxide ([N.sub.2]O). This study compared the effectiveness of three [N.sub.2]O scavenging systems, the Porter/Brown, the Accutron, and the Matrx, in actual time during use in a standardized mock dental treatment protocol that reflected clinical practice while minimizing the influence of confounding variables. At every occasion during the procedure, the Porter/Brown scavenger system left the operatory with significantly less [N.sub.2]O than any of the other scavengers tested. The Porter/Brown removed between 71% and 91% of the [N.sub.2]O compared to the control (no device).

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Introduced as an anesthetic in 1844, the analgesic, anxiolytic, and psychosedative properties of nitrous oxide ([N.sub.2]O) make it a nearly ideal agent for use in outpatient sedation for dental procedures. The ADA Council on Scientific Affairs and the ADA Council on Dental Practice have stated that "nitrous oxide continues to be a valuable agent for the control of pain and anxiety." (1) However, there are environmental health concerns for dental health care providers chronically exposed to trace amounts of waste [N.sub.2]O. Chronic [N.sub.2]O exposure has been linked to spontaneous abortion and reduced fertility, irritability, headache, nausea, congenital abnormalities, lymphoid malignancies, cervical cancer, and hepatic, renal, and neurological disease. (2-4)

Bruce and Bach investigated the effects of [N.sub.2]O exposure on operator performance. (5-7) They observed decreased psychomotor performance in visual perception, immediate memory, and cognitive and motor responses in human subjects receiving as little as 50 ppm [N.sub.2]O over a two hour period. (8) Subjects exposed to 25 ppm [N.sub.2]O did not demonstrate such effects. In a similar study, Cook found no changes in performance until the subjects were exposed to 20% [N.sub.2]O, or the equivalent of 200,000 ppm. (9)

The literature reveals a lack of agreement concerning safe limits for the ambient level of [N.sub.2]O. The National Institute of Occupational Safety and Health (NIOSH) recommends a maximum allowable time weighted average (TWA) of 25 ppm of total [N.sub.2]O exposure in both the operating room and the outpatient setting. (4) It was determined that 25 ppm was achievable in the operating room but not attainable in the dental operatory. Therefore, NIOSH chose 50 ppm to be the maximum exposure limit for personnel in the dental setting. (10) The American Conference of Governmental Industrial Hygienists recommends a [N.sub.2]O exposure limit of 50 ppm for an eight hour TWA. (10) Among the methods used to control [N.sub.2]O exposure in the dental office, the ADA emphasizes the routine use of scavenging equipment. (1,11) Levels of ambient [N.sub.2]O have been reported to be 300-1,000 ppm when scavenging units are not used. (12) Further, studies have shown that some scavenging systems do not consistently maintain the operator's breathing space to within safety standards. (13,14)

Few studies have compared the effectiveness of different [N.sub.2]O scavenging systems. (17) A number of variables related to the delivery of [N.sub.2]O sedation are difficult to control and complicate such studies. These include the type of dental procedure, mouth breathing, patient movement, mask fit, and quality of highspeed evacuation. (20-23) Previous studies have found the Porter/ Brown [N.sub.2]O scavenging system to be superior to others. (15-19) Donaldson reported that the mean ambient [N.sub.2]O level following use of the Porter/Brown device during a dental procedure was 43.4 ppm. (18) These studies, however, involved the collection of gases throughout the dental procedure and a TWA of the [N.sub.2]O at a specific time, not the actual time of exposure to [N.sub.2]O by the dental team.

The ADA has published recommendations for controlling [N.sub.2]O exposure. (1) The report stated that dental offices could control [N.sub.2]O exposure by implementing current recommendations on scavenging equipment maintenance and work practices. However, the level of [N.sub.2]O in dental offices that follow these recommendations has not been established. This study sought to compare the effectiveness of three [N.sub.2]O scavenging systems in actual time during their use in a standardized mock dental treatment protocol that reflected clinical practice while minimizing the influence of confounding variables. The hypothesis is that there is no difference in ambient [N.sub.2]O measurements between the three scavenger units during mock dental treatment.

MATERIALS AND METHODS

Three [N.sub.2]O scavenging devices were tested following a controlled clinical protocol. The scavenging devices differ in mask design. The Accutron Model No. 32203 Alpha MX (Accutron, Inc., Phoenix, AZ; 800/531-2221) and Matrx MDM (MDS Matrx, Orchard Park, NY; 800/847-1000) have one rubber nasal hood with a small plastic scavenging cap perched at the top of it (Figure 1). The Accutron is disposable after one usage; the Matrx can be autoclaved. The Porter/ Brown Model No. 2445-1 (Porter Instrument Company, Inc., Hatfield, PA; 800/457-2001) incorporates two rubber pieces into the mask design and can be autoclaved (Figure 1). The scavenging units are similar in that the mask is connected to a high evacuation tubing that evacuates ambient [N.sub.2]O and exhaled air at 45 L/minute out of the building.